An adjective, similar in meaning to ridiculous. Supposedly coined (but certainly popularized) by Adam Corolla on the late-night radio call-in show Loveline, this term has been around for a long time. It is a simple modification of the word rediculous, which contains the first three letters of the word dick. Replacing those letters with the first three letters of cock, another synonym for penis, yeilds ricoculous. There is no 'k' in 'ricoculous': the original isn't spelled "ridickulous", is it?
It is usually used as a more emphatic version of 'ridiculous', especially when the subject of ridicule is sexual in nature. "The idea that a nineteen-year-old male would turn down a blowjob is ricoculous!"
Other forms of ricoculous (e.g. ricoculousness) are rarely encountered.